1. Field of the Invention
The present invention relates to a grinding tool that uses a surface of a tool base on which abrasive grains are discretely provided, as a grinding surface, as well as a method and apparatus for picking up an image of the grinding surface of this grinding tool to inspect the conditions of the grinding surface on the basis of the image data obtained.
2. Description of the Related Art
In the field of grinding work, a non-porous grindstone or a porous grindstone is commonly used as a grinding tool. The non-porous grindstone has a grinding surface formed by using a binder 13 to stick abrasive grains 20 to a peripheral surface of a grindstone base 11, for example, as shown in FIG. 11. If such a grindstone 10 is used for grinding work, the grindstone 10, which is shaped like a disk or a cylinder, is rotated at a high speed in the direction of an arrow A, for example, as shown in FIG. 12. Then, a grinding surface of the grindstone 10 is abutted against a surface of workpiece 30 to be ground. Then, the workpiece 30 is moved at a constant speed in the direction of an arrow B. Thus, the ground surface of the workpiece 30 is cut to a fixed depth D by the abrasive grains 20. The surface of the workpiece 30 is thus ground. Reference numeral 31 denotes chips resulting from the cutting by the abrasive grains 20.
In grinding work of this kind, the finishing quality of the ground surface of the workpiece 30 depends on the condition of the grinding surface of the grindstone 10. The conditions of the grinding surface are primarily determined by the shape and size of the surface of each abrasive grain 20, functioning as a cutting edge, the distribution of the abrasive grains 20, and the amount of projection of each abrasive grain 20. Thus, large grinding streaks may remain on the ground surface of the workpiece depending on the conditions of the abrasive grains 20. FIG. 13 is a partial enlarged view showing an example of grinding streaks 32. Accordingly, to achieve high-quality grinding work, it is important to accurately determine the conditions of the grinding surface, i.e. the shape and size of the surface of each abrasive grain 20, the distribution of the abrasive grains 20, the amount of projection of each abrasive grain 20, and the like.
Thus, in the prior art, an image of the grinding surface is picked up using, for example, a metallurgical microscope of a high magnification provided with a camera. Then, image data obtained is subjected to predetermined image processing to create an image in which the abrasive grains 20 appear to stand out. Subsequently, the image is inspected. Efforts have hitherto been made to study such techniques.
However, the tip of each abrasive grain 20, which functions as a cutting edge, has a color density similar to that of the binder 13 covering the surface of the base 11. Thus, in the image data obtained, it is very difficult to use a difference in color density to make the tips of the abrasive grains 20 more conspicuous than the other parts such as the binder. Further, the tip of each abrasive grain 20 does not have a distinctive shape. It is thus also difficult to display the tips of the abrasive grains 20 so as to distinguish the tips from the other parts on the basis of their shapes. On the other hand, it has been contemplated that this problem may be solved by applying recent advanced image processing techniques. However, this method requires complicated image processing and a high-definition camera. This in turn requires an expensive large-scale system. Therefore, this method is not practical.
Furthermore, even if such a system is used to successfully display the abrasive grains 20, it is impossible to extract those of the abrasive grains 20 forming the grinding surface which are actually involved in the grinding work. It is thus difficult to determine the condition of the abrasive grains actually involved in the grinding work.